M81 and M82 - last night

Galaxies are beasts which require long exposures times and, as a result, I concur with the use of 15-min subs. Yes, a few stars may reach saturation but so what?

When imaging any object, my primary weapon is the histogram. With galaxies, these histograms are problematic in the sense that one has a lot of signal up to, for example, 20,000 ADU and then things become sporadic after that and it is mostly due to stars contributing a few bars past 20,000 ADU in the histogram.

Stacking will improve the final histogram but we must also remember that integrations in RGB will have even poorer histograms.

I agree that there seems to be a slight problem with the stars and I do not know if this is due to a change in seeing during the session, a change in focus due to a temperature drop etc but certainly I would not cut back on the 15-min subs and this is something especially critical for the RGB subs.

Cheers Lads.
To reduce the star sizes, I used a plugin/action in Photoshop called Astronomy Tools. For more info:
actions.home.att.net/Astronomy_Tools_For_Full_Version.html
Basically, it's a series of options which, when you select one, will run a series of commands to undertake that action. One of them is called "Make Stars Smaller" and, er, well, it does exactly that!

Regards,

Grand images, Can I ask how did you focus the camera?

Absolutely fantastic image. Loads of detail in the spiral of M81 (something I've never managed apart from a smudgy spiral).

Autoguiding must have worked a treat to get 15 minutes subs!

M82 looks great as well.

Mike,
just spotted this post now. I must say, you're really enjoying the new set up, and the images you're taking are really coming along. I can't wait to see if you can provide colour ones, but what you have done in b&w so far? Excellent...

Grand images, Can I ask how did you focus the camera?

Dave,
I'm using Robofocus and Maxim DL. I select a star and then adjust the focus using the hand controller. The ccd camera takes a series of exposures just around this star and refreshes them on the screen at intervals you decide on. Maxim then analyses the shape of the light curve from the star and generates a little graph along wioth some numbers. One of these numbers is the "FWD", if I remember correctly (full width diameter, I think). This gives a more accurate estimate of focus than FWHM, apparently. Once the value is as low as I can get it, I then start taking images.
Does this explain it clearly?

Regards,